Description (Abstract Provided by Applicant): We hypothesize that gender, ovulatory function and disease may affect P-glycoprotein (P-gp) expression in the intestine and other organs such as the liver, endometrium and lymphocytes, thereby modulating the effectiveness of protease inhibitors (PIs) in HIV+ women. P-gp expression and function varies with ovulatory function and phase. The highest levels occur during menopause and in the midluteal phase of the cycle; the severity of disease can also influence P-gp activity in various tissues in women (liver, gut, lymphocytes and endometrium). This in turn can affect the pharmacokinetics and pharmacodynamics of protease inhibitors (PIs) as well as the progression of HIV disease. While differences in pharmacokinetics of drugs that are cytochrome P4503A (CYP3A) and P-gp substrates, such as the PIs, are manifested as differences in metabolism, we believe that this end result is regulated by differences in P-gp function and activity rather than by differences in CYP3A expression across the population. Project IV has five specific aims: I) to determine if the intestine, like the liver and endometrium, exhibits variable levels of transporter and enzyme that are regulated by progestins and/or estrogen, (which will also serve as a measure as to how well commonly used cell lines, e.g., liver and endometrium, exhibit characteristics that may be useful in testing the hypothesis); 2) to learn whether an assay in lymphocytes might be used as a simple model for what occurs in the endometrium, intestine and liver; 3) to test whether known differences in P-gp between premenopausal and postmenopausal women translate into differences in PI drug levels; 4) to correlate ovulatory cycle phase (early follicular, midluteal and postmenopausal) and/or P1 levels with markers of viral resistance; and 5) to determine the effects of four parameters: (a) stage of ovulatory cycle phase (early follicular. midluteal or postmenopausal), (b) ethnicity (particularly African American vs. Caucasian), (c) presence vs. absence of HIV infection, and (d) CD4 count strata on P-gp expression, as measured by quantitative analysis of P-gp in tissue biopsies (intestinal cells, endometrium and peripheral blood mononuclear cells) and P-gp function, as measured by PT pharmacokinetic profiles.